The molecular basis for biological inactivation of nucleic acids. The action of methylating agents on the ribonucleic acid-containing bacteriophage R17

Shooter, K. V.; Howse, Ruth; Shah, S. A.; Lawley, P.D.

doi:10.1042/bj1370303

Cited by 56 publications

(21 citation statements)

References 27 publications

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“…DNA alkylation occurs due to reactions involving both S N 1 and S N 2 alkylating agents [25], and the susceptibility of each potential alkylation site on the bases or backbone varies on these reagents [2,6,25,26]. AlkB is responsible for repairing the damage caused by the S N 2 type methylating agents such as MMS and methyl halides.…”

Section: E Coli Alkbmentioning

confidence: 99%

“…AlkB is responsible for repairing the damage caused by the S N 2 type methylating agents such as MMS and methyl halides. These can react with single-stranded DNA (ssDNA) to generate large portions of N 1 -methyladenine (1-meA) and N 3 -methylcytosine (3-meC) [2,6,25,26] and they are the main methylation lesions formed [27][28][29]. These methyl adducts could be removed by two chemical mechanisms: (i) a direct displacement of the methyl group by a nucleophilic Cys residue or an activated water, which is similar to the mechanism used by the Ada proteins; or (ii) oxidation of the methyl group to give a hydroxyl intermediate, which decomposes in water to afford the repaired base and formaldehyde.…”

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confidence: 99%

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Oxidative dealkylation DNA repair mediated by the mononuclear non-heme iron AlkB proteins

Mishina

2006

Journal of Inorganic Biochemistry

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DNA can be damaged by various intracellular and environmental alkylating agents to produce alkylation base lesions. These base damages, if not repaired promptly, may cause genetic changes that lead to diseases such as cancer. Recently, it was discovered that some of the alkylation DNA base damage can be directly removed by a family of proteins called the AlkB proteins that utilize a mononuclear non-heme iron(II) and α-ketoglutarate as cofactor and cosubstrate. These proteins activate dioxygen and perform an unprecedented oxidative deal-kylation of the alkyl adducts on DNA heteroatoms. This review summarizes the discovery of this activity and the recent research advances in studying this unique DNA repair pathway. The focus is placed on the chemical mechanism and function of these proteins. KeywordsDNA repair; AlkB; ABH; Direct repair; Mononuclear non-heme iron; Dioxygenase; Oxidative dealkylation; Demethylation Direct repair of alkylation DNA damageCellular DNA is subject to nonenzymatic alkylation (methylation) by environmental or chemical mutagens, resulting in adducts that are toxic and mutagenic [1][2][3][4][5][6]. Organisms have evolved a variety of mechanisms to repair these mutagenic damages. Escherichia coli (E. coli) responds to this threat by activating an adaptive responsive pathway, mediated by the E. coli Ada protein [7]. Upon receiving a methyl group from the damaged DNA, Ada turns into a transcriptional activator and activates its own expression and that of the alkB gene and two other genes, alkA and aidB ( Fig. 1(a)) [4,7,8]. The upregulated Ada is a bifunctional protein, which uses a N-terminal Cys38 residue to remove a methyl group fromS p -methylphosphotriester and a C-terminal Cys321 residue to remove a methyl adduct from O 6 -methylguanaine ( Fig. 1(b)) [9][10][11]. Both repair functions are irreversible and represent rare examples of direct repair of DNA damage. AlkA is a glycosylase that cleaves methylated bases from DNA and performs the first step of the well-known base excision repair of base lesions [12][13][14]. The precise function of AidB is still unknown. The function of the last member of this adaptive response, AlkB, also remained unknown until recently despite extensive research efforts. E. coli AlkBSince the first genetic study in 1983 isolating the E. coli mutant with specific sensitivity to the alkylating agent methylmethane sulfonate, MMS [15], the activity of AlkB was undisclosed The Fe II /αKG-dependent dioxygenase superfamily is widespread from bacteria to humans [19] and is the largest known non-heme iron protein family [20][21][22][23]. It represents a wide diversity of enzymes that catalyze the hydroxylation of unactivated C-H groups of a variety of substrates by coupling reductive activation of dioxygen with a decarbox-ylation of αKG, the co-substrate, to succinate. In the event of oxidation one of the oxygen atoms from O 2 is incorporated into the succinate and the other as a hydroxyl in the product [24]. This group of enzymes is known for their importance in ...

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Section: E Coli Alkbmentioning

confidence: 99%

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confidence: 99%

Oxidative dealkylation DNA repair mediated by the mononuclear non-heme iron AlkB proteins

Mishina

2006

Journal of Inorganic Biochemistry

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“…The biological effect of ribophosphotriester formation has been assumed to be inactivation as a result of chain scission (11)(12)(13). We find, however, that as many as four phosphotriesters can be present in undegraded TMV RNA.…”

Section: Discussionmentioning

confidence: 45%

“…It has long been believed that, in contrast to deoxyribophosphotriesters, ribophosphotriesters were extremely unstable, and as soon as a triester was formed, chain scission occurred (10)(11)(12)(13). This was based primarily on indirect evidence, since no ribophosphotriester had been isolated or synthesized while deoxyribophosphotriesters had been synthesized and found to be stable under a variety of conditions (14)(15)(16).…”

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confidence: 99%

Effects of alkylation of phosphodiesters and of bases of infectivity and stability of tobacco mosaic virus RNA.

B¹,

Sun²,

Fraenkel‐Conrat³

1975

Proc. Natl. Acad. Sci. U.S.A.

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Upon ethyl nitrosourea treatment of RNA of tobacco mosaic virus, up to four phosphodiester groups may be alkylated per molecule without chain breakage, as shown by sucrose gradient centrifugation. This indicates that ribophosphotriesters are quite stable. However, when this alkylation reaction is of longer duration and 6 to 10 triesters are formed, then an average of 1 to 2 breaks occurs and little or no intact RNA can be isolated. Methyl nitrosourea is less effective in forming triesters (about 25% of total alkyl groups compared to about 65% for ethyl nitrosourea), and a greater number of alkyl groups can, therefore, be introduced before breaks occur. Diethyl sulfate and dimethyl sulfate, which alkylate almost only the bases of nucleic acids, do not cause significant degradation of RNA of tobacco mosaic virus, even when as many as 70 alkyl groups are bound.All types of alkylation cause similar losses in viral infectivity at low levels of alkylation. Thus, an average of two chemical events leads to one lethal event, regardless of the nature of the alkylating reaction, which, for example, is with dimethyl sulfate about 65% on the N-7 guanine while with ethyl nitrosourea it is about 65% on phosphodiesters. It is thus concluded that all alkyl groups, whether on the base or on the phosphate, have the same potential to cause inactivation and that inactivation of RNA can result from phosphotriester formation per se.Alkylation of nucleic acids by ethyl nitrosourea (EtNU) in neutral aqueous solution has been shown to occur primarily on the 06 of guanine and on the oxygen of phosphodiesters (1, 2). About 65% of the total alkylation of RNA in vitro and of HeLa cell DNA in vitro and in vivo is in the form of phosphotriesters, while 8-12% is in the form of 06-ethylguanine (1, 2). EtNU is a very potent carcinogen (3, 4), and the mechanism of its biological effect has been studied by Goth and Rajewsky (5-7), Lijinsky et al. (8), and Swann and Magee (9). All agree that there is no correlation between tumor formation in rats and the amount of 7-ethylguanine found in the RNA or DNA of various tissues. Goth and Rajewsky (6,7) propose that ethylation of the 06 of guanine is the significant biological event, but they do not consider phosphate alkylation, although their data can now be interpreted as indicating about 70% phosphotriester formation (1,2).In the course of a general study of the alkylation of nucleic acids, this laboratory has now focused on the chemical and biological effects of phosphate alkylation. In this paper we present data on the stability of ribophosphotriesters in tobacco mosaic virus (TMV) RNA and the effects of triester formation on the infectivity of intact (30S) TMV RNA.It has long been believed that, in contrast to deoxyribophosphotriesters, ribophosphotriesters were extremely unstable, and as soon as a triester was formed, chain scission occurred (10-13). This was based primarily on indirect evidence, since no ribophosphotriester had been isolated or synthesized while deoxyribophosphotriesters ha...

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“…DMN and NMU give rise to both these methylated bases, whereas no 06-methylguanine was detectable in rat liver after treatment with MMS (Craddock, 1973b). A small amount was measured after treatment of DNA with MMS in vitro (Lawley and Shah, 1972), and in mice treated with MMS in vivo (Frei and Lawley, 1976 proportion of the products of reaction with nucleic acids (Shooter et al, 1974;Lawley, Orr and Jarman, 1975;Singer and Fraenkel-Conrat, 1975;Sun and Singer, 1975). To investigate further whether replication of DNA containing 06-alkylated guanine residues could be responsible for carcinogenesis, it was of interest to determine whether EMS induced liver-cell cancer when given to animals in which liver cells had been stimulated to proliferate by partial hepatectomy.…”

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confidence: 97%

Induction of tumours in intact and partially hepatectomized rats with ethyl methanesulphonate

Craddock¹,

Frei²

1976

Br J Cancer

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The molecular basis for biological inactivation of nucleic acids. The action of methylating agents on the ribonucleic acid-containing bacteriophage R17

Cited by 56 publications

References 27 publications

Oxidative dealkylation DNA repair mediated by the mononuclear non-heme iron AlkB proteins

Oxidative dealkylation DNA repair mediated by the mononuclear non-heme iron AlkB proteins

Effects of alkylation of phosphodiesters and of bases of infectivity and stability of tobacco mosaic virus RNA.

Induction of tumours in intact and partially hepatectomized rats with ethyl methanesulphonate

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